Non-aqueous lithium electrochemical cells typically include an anode, a lithium electrolyte prepared from a lithium salt dissolved in one or more organic solvents and a cathode of an electrochemically active material, typically a chalcogenide of a transition metal. During discharge, lithium ions from the anode pass through the liquid electrolyte to the electrochemically active material of the cathode where the ions are taken up with the simultaneous release of electrical energy. During charging, the flow of ions is reversed so that lithium ions pass from the electrochemically active cathode material through the electrolyte and are plated back onto the lithium anode.
Recently, the lithium metal anode has been replaced with a carbon anode such as coke or graphite intercalated with lithium ions to form Li.sub.x C.sub.6. In the operation of the cell, lithium passes from the carbon through the electrolyte to the cathode where it is taken up just as in a cell with a metallic lithium anode. During recharge, the lithium is transferred back to the anode where it reintercalates into the carbon. Because no metallic lithium is present in the cell, melting of the anode does not occur even under abusive conditions. Also, because lithium is reincorporated into the anode by intercalation rather than by plating, dendritic and spongy lithium growth does not occur. Non-aqueous lithium electrochemical cells are discussed, for example, in U.S. Pat. Nos. 4,472,487, 4,668,595 and 5,028,500. These cells are often referred to as "rocking chair" batteries because lithium ions move back and forth between the intercalation compounds during charge/discharge cycles.
U.S. Patent 4,770,960 reports a lithium liquid electrolyte cell using a cathode active material which is the complex oxide LiCo.sub.1-x Ni.sub.x O.sub.2 made from calcined mixtures of Li.sub.2 CO.sub.3, CoCO.sub.3 and NiCO.sub.3. In such cells, the discharge capacity decreases with the increase in nickel content for x&gt;0.27. The recommended cathode active materials are therefore those having 0&lt;x.ltoreq.0.27.
U.S. Pat. No. 5,053,297 discloses cathode active materials which contain as a primary active material a first lithium compound having an electrochemical potential which is more noble than the electrochemical potential of the current collector, and an auxiliary active material which is a second lithium compound having an electrochemical potential which is more base than the electrochemical potential of the current collector. Examples include physical mixtures of LiNiO.sub.2 and LiCoO.sub.2, as well as, chemical mixtures i.e. LiNi.sub.0.95 Co.sub.0.05 O.sub.2, for use in lithium liquid electrochemical cells. The electrolyte may alternatively be a gel electrolyte. The addition of auxiliary active material decreases the battery energy density. The preferred anode is a carbon material.
European parent application 91119471.0 (Publication 0486950A1) discloses a liquid electrolyte secondary lithium cell having an intercalation carbon anode and a cathode which comprises a lithium-containing metal complex oxide of the formula Li.sub.x MO.sub.2, wherein x is 0.5.ltoreq.x.ltoreq.1 and M is selected from the group Co, Ni and Mn. Examples of the metal complex oxides include LiCoO.sub.2, LiNiO.sub.2, LiNi.sub.y Co.sub.1-y O.sub.2, (O&lt;y&lt;1), LiMn.sub.2 O.sub.4 and mixtures thereof. The cathode active material is ordinarily used in combination with a conductive agent such as graphite and a binder therefor such as polyvinylidene fluoride. The average discharge voltage of the cell is about 3.6 volts.
U.S. Pat. No. 5,429,890 discloses a secondary lithium electrochemical cell having a cathode which comprises a physical mixture of Li.sub.x M.sub.n O.sub.2 (Spinel) and at least one lithiated metal oxide selected from Li.sub.x NiO.sub.2 and Li.sub.x CoO.sub.2, wherein 0&lt;x.ltoreq.2. The disclosures of each of the foregoing references is incorporated herein in its entirety.
While the technology involving rocking chair batteries has provided the industry with a viable alternative, potential drawbacks to rocking chair batteries, however, include lower energy density compared to lithium metal cells. Providing new high capacity, high voltage cathode materials would help to overcome such drawbacks and could provide the industry with an even more powerful and useful battery.
It is therefore an object of the present invention to provide a novel cathode material which can provide high capacity, high voltage batteries.
Another object of the present invention is to provide such high capacity batteries.
These and other objects of the present invention will become apparent upon a review of the following specification and the claims appended thereto.